Mark Foster is a main character on ABC family comedy Step by Step. He is portrayed by Christopher Castile.

Character Edit

Carol's only son and the youngest child in the family, who is depicted as a nerd, and is into computers and academics. Later on, he matures to be "a normal teenager" and has friends and a girlfriend, while still a high academic achiever. He seems to be somewhat similar to Steve Urkel, although Mark has not proposed as many outlandish inventions. In a crossover with Family Matters, Mark works with Steve Urkel on a science project for a national competition.